Conventionally, compressors are provided in, for example, air conditioners and have been used for compressing refrigerant in refrigerant circuits. In the compressors of this kind, there are known a rotary compressor of which hermetic casing accommodates a compression mechanism and an electric motor for driving the compression mechanism.
In the compression mechanism, a piston slews in a cylinder chamber by driving the electric motor. In association with the slewing motion, refrigerant at low pressure is sucked into a suction chamber through a suction port while refrigerant in a compression chamber becomes high pressure and is discharged into the inside of the casing through a discharge port.
Generally, a reed valve and a valve retainer for the reed valve are provided at the discharge port. When the compression chamber becomes a predetermined pressure or higher, the reed valve is warned at its valve body on the tip end side thereof to open the discharge port. When the refrigerant has been discharged from the compression chamber into the inside of the casing, the reed valve closes the discharge port by spring force of its own. The valve retainer fixes at the base end thereof the reed valve and restricts at the tip end thereof the valve body of the reed valve to a warp amount (a lift amount).
In the above compressor, the reed valve is warped largely especially in a high speed operation, namely, the lift amount of the reed valve becomes large, causing generally-called closing delay where the discharge port is not immediately closed when the compression chamber is exchanged from high pressure to low pressure. This causes the refrigerant at high pressure to flow back into the compression chamber from the inside of the casing, thereby lowering volumetric efficiency.
For tackling the above problem, Japanese Utility Model Registration Application Laid Open Publication No. 61-138881A, for example, proposes a valve retainer having a tip end part made of a bimetal. Specifically, the face portion at the tip end of the valve retainer on the opposite side to the reed valve side is made of a bimetal. In this compressor, the discharge temperature of the refrigerant rises as the operation speed is increased. The bimetal is warped in a direction separating from the discharge port in association with increase in discharge temperature. This changes the reed valve supporting state of the valve retainer to increase the spring constant (spring force) of the reed valve, allowing the reed valve to start closing earlier. As a result, the closing delay of the reed valve in a high speed operation is suppressed.
—Problems to be Solved—
However, in the above compressor, the valve retainer is warped depending only on change in discharge temperature, resulting in less reliability. Further, the lift amount of the reed valve is difficult to adjust in response to the discharge rate, inviting discharge pressure loss. In view of the foregoing, it has been desired to change the opening/closing state of the reed valve appropriate to the volume.
The present invention has been made in view of the foregoing and has its object of improving operation efficiency by controlling the opening/closing state of the reed valve appropriately to the volume.